Ovarian hormones are hypothesized to influence mood, motivation and behavior in humans. Due to endocrinological similarities with humans, the rhesus monkey is a popopular animal model for investigating these relationships. However, much of the previous research on these questions has suffered from one or more methodological deficiencies. The present studies are designed to overcome these deficiencies. Through behavioral observations of pair mating under laboratory conditions, the present studies use Psychobiological techniques to focus on proceptive behaviors of rhesus females, i.e., those female behaviors that act as sexual invitations and are thought to reflect female mood and sexual motivation. Behavioral sequences of time limited sexual encounters between male and female pairs are videtaped and later scored. In addition, radioimmunoassay of female plasma is used to establish circulating levels of ovarian hormones during menstrual cycles and after various hormone treatments. The three studies outlined seek to: a) identify female behaviors which function as sexual invitations and therefore could be classified as proceptive behaviors; b) determine, by utilizing measurement of circulating hormones to align cycle stages, whether the display of proceptive behaviors is influenced by normal endocrine changes across the menstrual cycle; c) establish replacement therapies which induce physiological levels of ovarian hormones in ovariectomized females; and d) determine whether treatment of ovariectomized females with physiological levels of specific hormones can influence display of female proceptive behaviors. Preliminary results from these studies support the hypothesis that estrogens rather than androgens, are the primary steroid forms influencing rhesus female sexual motivation. Initial analyses also indicate that it will be necessary to pay particular attention to specific behavioral components, their sequencing, and the context in which they occur in order to understand the relationships between hormones and proceptive behaviors of rhesus monkeys. The results of these studies have implications concerning the potential for steroid hormones to influence mood, motivation, and behavior during the human menstrual cycle and in response to therapies given to agonadal and postmenopausal women.